“Hello. We are looking for highly intelligent individuals,” the message from “3301” said. “To find them, we have devised a test. There is a message hidden in this image. Find it, and it will lead you on the road to finding us. We look forward to meeting the few that will make it all the way through. Good luck.”

Mr. Eriksson, along with thousands of code breakers and IT enthusiasts throughout the world, have tried their hand at finding the information hidden within the digital file and following the rabbit hole to its source.

Along the way, those who took a seemingly wrong turn found images of a duck with the message: “Woops! Just decoys this way. Looks like you can’t guess how to get the message out.” It later turned out that important clues were embedded within the decoy message.

According to The Telegraph, the challenge — known as Cicada 3301 — has led “thousands of competitors across the web, down telephone lines, out to several physical locations around the globe, and into unchartered areas of the ‘darknet.’ So far, the hunt has required a knowledge of number theory, philosophy and classical music. An interest in both cyberpunk literature and the Victorian occult has also come in handy as has an understanding of Mayan numerology.”

Clues have led hunters to locations in Arizona, California, Paris, Seoul, Sydney and Warsaw, among others. As the challenged has progressed, so have the skills needed to continue. The ability to deal with hexadecimal characters, reverse-engineering and prime numbers is a must, Mr. Eriksson told The Telegraph.

The challenge is ongoing, having led users into the “darknet,” which the Telegraph estimates to be “5,000 times larger” than the “surface” web. It is also where drug cartels and terrorist organizations tend to reside.